This invention relates generally to a diode for generating an Intense Relativistic Electron Beam (IREB), and more particularly to a foilless diode that uses an ionized channel to generate an IREB.
IREB's are short (10's of nanoseconds) pulses of very high voltage (MeV) and high current (10k's of Amperes) electrons. They are useful for radiography, laser pumping, microwave generation, beam propagation and basic physics research, etc.
All IREB generators have a cathode for generating the high power electrons towards an anode. Prior art generators either have a large magnet for focussing the electrons away from the anode and into a beam, or a thin metal foil for diverting the electrons from the anode, permitting them to pass down the channel. Additional information on these generators is provided by R. B. Miller, An Introduction to the Physics of Intense Charge Particle Beams, Plenum Press, New York, 1982.
The use of magnets makes the IREB generator large and expensive, and the magnetic field gives the beam angular mosentum that causes an undesirable rotation of the IREB.
The use of a foil in the generator enables the magnets to be removed, but introduces a short circuit in the radial electric field causing an undesirable increase in the electron velocity perpendicular to the desired direction of the electron beam.
It is known that when an electron beam is injected into a preionized channel, the beam space charge ejects plasma electrons, leaving an ion core which electrostatically attracts electrons to the ion channel.
D. S. Prono, et al., Electron-Beam Guiding and Phase-Mix Damping by Electrostatically Charged Wire, Physical Review Letters, Vol. 51, No. 9, Aug. 29, 1983, pp. 723-726, discusses two experiments where a positive line charge was formed along a charged graphite wire supported on graphite foils. Prono's beam was generated in a conventional manner, accelerated and transported magnetically to the experiment. Prono found the charged wire to focus and damp the beam along the wire.
W. E. Martin, et al., Electron-Beam Guiding and Phase-Mix Damping by a Laser-Ionized Channel, Physical Review Letters, Vol 54, No. 7, Feb. 18, 1985, pp. 685-688, reported the use of a laser-ionized channel for relativisitic electron beam guiding, focusing and damping. They found the channel radius should be smaller than the beam radius for the radial focusing force to be anharmonic and thereby lead to desirable phase-mix damping of the transverse beam motion. They also found the electron beams density should be greater than the channel-ionization density to prevent instability. They used a conventional source to generate their IREB.